The present invention relates to a rubber composition, in which reaction efficiency of a silane coupling agent and various physical properties are improved.
Recently, the compatibility of lowering fuel costs and improving wet grip performance of a tire has been intensively desired, and in order to satisfy the request, compounding silica in a tire tread is carried out. However, since only silica cannot provide sufficient reinforcing property, a silane coupling agent is used in combination at the same time with silica. In particular, a silane coupling agent containing an alkoxy group is generally used for tire use. However, the reaction of the silane coupling agent cannot be adequately completed at a step of kneading a rubber, and there is no other choice but the silane coupling agent more than necessity is compounded for obtaining sufficient reinforcing property. Further, there has been a problem that the silane coupling agent which could not be completely reacted during kneading (hereinafter, referred to as an unreacted silane coupling agent) is reacted in an extrusion step to generate alcohol (such as ethanol), which causes air bubbles generated in an extruded unvulcanized tread.
As a process to solve the problem, JP-A-2001-247718 discloses that various sodium salts are compounded in a rubber composition. Although the reaction efficiency of a silane coupling agent can be improved by the process, it is not sufficient, and the generation of air bubbles in an extrusion tread could not be perfectly suppressed.